25 June 2016

Pioneering techniques could settle longstanding controversy about the accuracy of previous simulations

For the first time, cosmologists have used the full power of Albert Einstein's general theory of relativity to perform detailed calculations of the Universe’s evolution.

The two groups’ techniques—which break with nearly a century of tradition—could help to settle a controversy over the accuracy of previous, simplified simulations, and could help researchers to interpret the results of astronomers’ increasingly precise observations.

General relativity interprets gravity as the warping of space-time. Soon after Einstein proposed his theory in 1915, others realized that it had dramatic implications on the cosmic scale. Belgian cosmologist Georges Lemaître and others pointed out in the 1920s that a Universe that satisfies Einstein’s theory should either expand or contract. (Meanwhile, astronomer Edwin Hubble and others showed that it was, in fact, expanding.)

But solving Einstein’s equations on a cosmic scale was impossible without making assumptions to simplify the calculations. To reach their conclusions, Lemaître and the other early relativists assumed that matter was uniformly distributed as a continuum across space, rather than being concentrated in stars and galaxies.

A MATTER OF DISTRIBUTION

The advent of technology did not substantially change the situation, because the full relativistic calculations were difficult even for supercomputers. Most cosmologists have continued to model the Universe, starting with the Big Bang, in this way. To explain how large structures such as galaxies and clusters of galaxies form from a diffuse primordial gas, researchers start with regions of slight 'overdensity', which then develop into lumpy structures under the pull of gravity. Such models, however, assume an uneven spread of matter only for the relatively small area that they are studying—while maintaining a uniform distribution on the largest scales.

Some cosmologists say that this was more of a necessary stratagem than a well-justified assumption. “The homogeneity of the Universe is a philosophical invention,” says Sabino Matarrese, a general-relativity theorist at the University of Padua in Italy. In the past decade or so, Matarrese and others have argued that this assumption might even have led astronomers to misinterpret their data when they concluded that the Universe’s expansion has been accelerating under the action of a mysterious ‘dark energy’.

This, he says, triggered a heated debate. But, he adds, the assumption of homogeneity “is, in part, circular reasoning, which we could try to question without getting into drama”.

Numerical relativist Eloisa Bentivegna of the University of Catania, Italy, says that, “in principle, in an inhomogeneous Universe, distant galaxies could appear as if they were receding at an accelerated pace,” mimicking the effects of dark energy.

COMING TOGETHER

Now, she and Marco Bruni of the University of Portsmouth, UK, and independently Glenn Starkman of Case Western Reserve University in Cleveland, Ohio, and his colleagues, have performed the first full simulations of a Universe that follows general relativity without restrictions. Each group used supercomputers to model how an early Universe expands and how its warping evolves as matter begins to gather in large pools under the force of gravity, leaving other regions with more-rarefied gas.

Their papers, which appear on June 24 in Physical Review Letters and in Physical Review D, still do not reproduce the full complexity of the actual Universe, but their full embrace of relativity is “revolutionary,”says Matarrese.

The two groups used slightly different techniques with an emphasis on different questions: the Europeans focused more on the formation of 'overdense' structures, whereas the US group concentrated on how the Universe expands and how its curvature affects the propagation of light. Both teams say that, in the future, they plan to increase the sophistication of their models and to connect them to quantities that astronomers can actually measure.

Both groups built on numerical-simulation techniques that had been developed for calculating the warping of space-time around pairs of mutually orbiting black holes and the resulting gravitational waves—the very predictions that were confirmed earlier this year by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO). “It’s a marriage between numerical relativity and cosmology that hasn't happened before,” says Starkman.

It will take perhaps two decades to unravel the potential of these techniques, Matarrese says. He and others say that—while dark energy is probably here to stay—researchers will need increasingly precise predictions to interpret the results of upcoming big-science observatories. These will include data from the Square Kilometer Array in Australia and South Africa.

The big question is whether the pooling of matter in dense regions—and the subsequent formation of galaxies—can have effects on the overall expansion of the Universe. This 'back-reaction' effect might be tested by next-generation experiments, something that would be a “great triumph,” says cosmologist Scott Dodelson of the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois. But, he says, it is unclear yet whether the teams' techniques are necessary to understand such effects, or if the more conventional methods suffice.

Starkman expects that, in the end, as far as the big picture is concerned, the standard model of cosmology will hold—including the existence of dark energy. “But we have to check.”

Parrhesia

The two all-time most popular posts of Transudationism

A modern-day classic

All life is a form of light, and the cosmos is a holonic Holy Hologram.

Immanence ≋ Transcendence

Transudationism: mankinds' cosmic ideology.

SIC ITUR AD ASTRA!

Ascensional Transudation

Cosmic Evolution

All history is the history of the evolutionary transubstantiation of matter to Spirit via biological-life processes of Blood and Reason.

Alexandr Solzhenitsyn's concluding thoughts from his 1978 Harvard address, A World Split Apart

Alexandr Solzhenitsyn's concluding thoughts from his famous 1978 Harvard address,"A World Split Apart":

It would be retrogression to attach oneself today to the ossified formulas of the Enlightenment. Social dogmatism leaves us completely helpless in front of the trials of our times.

Even if we are spared destruction by war, our lives will have to change if we want to save life from self-destruction. We cannot avoid revising the fundamental definitions of human life and human society. Is it true that man is above everything? Is there no Superior Spirit above him? Is it right that man's life and society's activities have to be determined by material expansion in the first place? Is it permissible to promote such expansion to the detriment of our spiritual integrity?

If the world has not come to its end, it has approached a major turn in history, equal in importance to the turn from the Middle Ages to the Renaissance. It will exact from us a spiritual upsurge, we shall have to rise to a new height of vision, to a new level of life where our physical nature will not be cursed as in the Middle Ages, but, even more importantly, our spiritual being will not be trampled upon as in the Modern era.

This ascension will be similar to climbing onto the next anthropologic stage. No one on earth has any other way left but - upward.

In recent times it has been fashionable to talk of the levelling of nations, of the disappearance of different races in the melting-pot of contemporary civilization. I do not agree with this opinion, but its discussion remains another question. Here it is merely fitting to say that the disappearance of nations would have impoverished us no less than if all men had become alike, with one personality and one face. Nations are the wealth of mankind, its collective personalities; the very least of them wears its own special colours and bears within itself a special facet of divine intention.

Dr. Paul Craig Roberts

Neoconservatives used 9/11 to launch their plan for US world hegemony. Their plan fit with the interests of America’s ruling oligarchies. Wars are good for the profits of the military/security complex, about which President Eisenhower warned us in vain a half century ago. American hegemony is good for the oil industry’s control over resources and resource flows. The transformation of the Middle East into a vast American puppet state serves well the Israel Lobby’s Zionist aspirations for Israeli territorial expansion.

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MIdwest Book Review:

"The seed of the universe is the big bang, says Kyle McDermott in 'The Declaration of White Independence: The Founding Documents of Transudationism'. An explanation of this view which holds that all of current humanity and life on Earth today was intentionally set in motion all those billions of years ago, 'The Declaration of White Independence' probes matters of cosmological significance with straightforward candor and accessibility. Featuring intriguing concepts and ideas, 'The Declaration of White Independence' is highly recommended for metaphysical studies shelves."

The Music of Life: Biology Beyond Genes

and speaking of cosmic symphonies, Julianne Hough

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